Hydrodynamic focusing for a micromachined flow cytometer

This paper describes hydrodynamic focusing inside a micromachined flow cyto meter. Flow cytometry is a process whereby cells are analyzed and sorted ba sed on hydrodynamic focusing phenomenon and specific cellular characteristi cs. In this study, the hydrodynamic focusing phenomenon is first modeled by employing potential flow theory Then the flow field inside the flow cytome ter is numerically simulated. The effect of the device geometry and relativ e sheath and sample flow rate on the focusing of the center flow is explore d systematically. At last, a micromachine-based flow chamber is designed an d fabricated on plastic substrates as a microflow cytometer. Hydrodynamic f ocusing is verified with the use of microscopic visualization of water shea th flows and dye-containing sample flow. Experimental data indicate that th e size of focused sample stream can be reduced to about 3 mum, which is app licable to cell sorting and counting.